Photographic emulsions containing 2-heterocyclic benzimidazole antifoggants



United States Patent 3,137,578 PHDTGGRAPi-IIC EMULSIGNS CONTAINING 2- HETERGCYCLIC BENZIMHDAZOLE ANTIFOG- GANTS Roy C. De Selms, Berkeley, Calif., assignor to Eastman Kodak Company, Rochester, N.Y., a corporation of New Jersey No Drawing. Filed Feb. 7, 1962, Ser. No. 171,585 8 Ciaims. (Cl. 96109) This invention relates to stabilized photographic com positions, and more particularly, to photographic silver halide emulsions containing novel fog-inhibiting agents.

It is well known that photographicemulsions on storage tend to lose sensitivity and to become spontaneously developable Without exposure to light. There is normally a detectable amount of the silver salt reduced during development in the areas where no exposure was given, this commonly being called fog, and sometimes chemical fog where it is necessary to distinguish between it and the efiects of accidental exposure to radiation. In this invention, I am not concerned with the latter.

Fog depends both on the emulsion and the conditions of development. For a given emulsion fog increases with the degree of development. With constant development conditions, fog tends to increase with time, temperature and relative humidity of storage conditions. It is common practice to make accelerated tests of the stability of photographic emulsions by storage at increased temperature or humidity, or both. It is of course, desirable to have emulsions as stable as possible under the conditions of high temperature and humidity which may occur in tropical climates, for example. Fog usually appears over the whole area of the sensitive coating, but when severe, it frequently is non-uniform. Fog may also be caused by exposure to chemicals, for example, hydrogen sulfide and other reactive sulfur compounds, hydrogen peroxide vapor, and strong reducing materials. While antifoggants and stabilizers may protect, to some extent, against such efiects, it is normally understood that an antifoggant protects against spontaneous growth of fog during prolonged storage or storage at high temperatures and humidities, or during development to maXimum contrast and speed, or both.

It is hence an object of this invention to inhibit fog formation in photographic silver halide emulsions with novel emulsion addenda.

It is also an object of this invention to provide new photographic silver halide emulsions containing antifoggant addenda that do not cause objectionable desensitization of the emulsion.

These and other objects of the invention are accomplished by incorporating into photographic silver halide emulsions benzimidazoles substituted in the 2-position by a heterocyclic radical wherein the NH moiety of the benzimidazole nucleus is separated from heteroatom of the heterocyclic substituent by two carbon atoms. Illustrative substituted benzimidazole emulsion addenda of the invention have the following structural formula:

CH N

3,137,578 Patented June 16, 1964 and Y represents the necessary carbon and hydrogen atoms to complete the heterocyclic ring, Y typically comprising 3 to 4 carbon atoms. Typical heterocyclic substituents for R include Z-thienyl, Z-thiopyranyl, 2-thiotetrahydropyranyl, Z furyl, Z-tetrahydrofuryl, 2-pyanyl, Z-tetrahydropyranyl, 2-pyrrolyl and the like.

The addenda of the invention described above can be added to photographic silver halide emulsions for purposes of increasing the stability thereof. More specifically the subject addenda serve as emulsion antifoggants. Many antifoggant addenda cause substantial desensitization or loss in speed of the emulsion when employed therein in antifoggant amounts. However, with the subject addenda there is no substantial loss of speed imparted to emulsions.

The particular quantity of the present stabilizers used in a given emulsion can vary, depending upon the eifects desired, degree of ripening, silver content of the emulsion, etc. I have found that generally from about .001 to 10 grams per mole of silver halide are quite adequate to accomplish the desired stabilization. Exposure of the treated emulsion in conventional photographic testing apparatus, such as an intensity scale sensitometer, will reveal the most advantageous concentrations for the present stabilizers in that particular emulsion. Such techniques are well understood by those skilled in the art.

The addenda of the invention can be added to photographic emulsions using any of the well-known techniques in emulsion making. For example, they can be dissolved in a suitable solvent and added to the silver halide emulsion, or they can be added to the emulsion in the form of a dispersion similar to the technique used to incorporate certain types of color-forming compounds (couplers) in a photographic emulsion. Techniques of this type are described in Jelley et al. US. Patent 2,322,- 027, issued June 15, 1943, and Fierke et al. US. Patent 2,801,171, issued July 30, 1957. The solvent should be selected so that it has no harmful effect upon the emulsion in accordance with usual practice, and generally solvents or diluents which are miscible with Water are to be preferred. Water alone is a dispersing medium for some of the stabilizers of the invention. In other cases, the subject stabilizers can be dissolved in solvents, such as ethanol, acetone, pyridine, N,N-dimethylformamide, etc., and added to the emulsion inthis form.

In addition to the subject antifoggant addenda, the photographic emulsions of the invention can contain the usual well-known emulsion addenda such as optical sensitizers, speed increasing materials, coating aids, gelatin hardeners, plasticizers and the like.

The stabilizer addenda of the invention can be used in various kinds of photographic emulsions. In addition to being useful in orthochromatic, panchromatic, and infrared sensitive emulsions, they are also useful in X-ray and other non-optically sensitized emulsions. They can be added to the emulsion before or after any optical sensitizing dyes which may be used. Various silver salts can be used as the sensitive salt such as silver bromide, silver iodide, silver chloride, or mixed silver halides such as silver chlorobromide or silver bromoiodide. The subject addenda can be used in emulsions intended for color photography, forexample, emulsions containing colorforming couplers or emulsions tobe developed by solutions containing couplers 'or other color-generating materials.

In the preparation of the silver halide dispersions employed for preparing silver halide emulsions, there can be employed as the dispersing agent for the silver halide in its preparation, gelatin or some other colloidal material such as colloidal albumin, a cellulose derivative, or a synthetic resin, for instance, a polyvinyl compound, although gelatin is preferred.

The above-described emulsions of the invention can be coated on a wide variety of supports in accordance with usual practice. Typical supports for photographic elements of the invention include cellulose nitrate film, cellulose acetate film, polyvinyl acetal film, polystyrene film, polyethylene terephthalate film and related films or resinous materials, as well as glass, paper, metals, wood and others.

Several benzimidazole derivatives of the invention were prepared and incorporated into photographic silver halide emulsions at varying concentrations and thereafter tested as antifoggants. The structural formulas of these prepared addenda of the invention are lettered and listed below, the letters given the addenda below being used for purposes of convenience of reference to indicate these adenda in the table of Example 1 below.

COMPOUND A 2-(2-tetrahydropyranyl) benzimidnzole COMPOUND B 2 (2'pyrro1y1) benzimidazole COMPOUND c 2-(2-thienyl)benzimidazole COMPOUND D 2- (2-tetrahydrofuryl) benzimidazole COMPOUND E 2-( 2fury1)benzimidazole Example 1 Typical benzimidazole stabilizers of the invention were incorporated into sulfur and gold sensitized high speed negative-type gelatino-bromoiodide emulsions which were panchromatically sensitized with a cyanine dye, and thereafter the emulsions were coated on cellulose acetate film supports. Similar photographic elements were prepared without the benzimidazole addenda for purposes of comparison. Samples of the prepared photographic elements were then incubated for 7 days at 120 F. and 50% relative humidity, and then exposed in the form of film strips in an Eastman Ib sensitometer, developed for 5 minutes at 68 F., and then fixed, washed and dried in the usual manner. Test samples were also exposed in the sensitometer directly after coating for purposes of comparison. The developer had the following fornula:

N-methyl-p-aminophenol sulfate 2.5 Hydroquinone 2.5 Sodium sulfite (anhydrous) 30.0 Sodium metaborate octahydrate 10.0 Potassium bromide 0.5

Water to make one liter.

The results of the sensitometric tests are summarized by the data set out in the table below with respect to relative speed, gamma and fog. In the table below the speeds indicated are a function of the exposure necessary to give a density of 0.2 above background fog, the initial control speed being taken as 100 in each case; and the concentrations of addenda are indicated as grams of addenda per mole of silver halide.

TABLE Cone. of Initial Test; 7 Days, 120 1? Addenda 50% R.H. Addenda (grams/ mole of AgX) Speed 7 F0 Speed 7 Fog O 100 1.15 11 07 1.13 19 3. 0 1. 18 .09 74 1.00 .12 6.0 71 1.10 .08 60 0. 97 .09 1. 5 01 1.18 .10 74 0. 97 14 3. 0 69 0. 98 09 62 0. .12 0 1.38 .13 62 0. 98 .35 Compound 0-- 3. 0 80 1. 47 12 87 1. 15 .16 D0 6. 0 83 1. 55 12 82 1. 20 14 Control 0 100 1. 25 13 80 1. 03 32 Compound D 0. 9 97 1. 30 12 78 1. 03 24 Do. 3. 0 100 1. 80 11 91 1.13 .18 Do 8. 7 89 1. 20 .11 87 1.13 .14 Control 0 100 1. 17 11 37 0.72 53 Compound E 3. O 76 1. O8 11 78 O. 98 .15

As can be observed from the data set out in the above table the 2-substituted benzimidazoles of the invention impart substantial antifoggant or stabilizing properties to photographic silver halide emulsions. Also to be noted is that there is no accompanying substantial loss in speed With the improved stability in the present instance, and which speed loss characterizes many antifoggants and many other photographic emulsion addenda.

To illustrate the high degree of unpredictability in the present art, I prepared and tested other photographic elements as described in Example 1 except that benzirnidazoles other than those of the invention were utilized. The benzimidazoles, Z-aminobenzimidazole and o-nitrobenzimidazole, were tested at concentrations of 0.3, 0.9 and 3.0 grams per mole of silver halide in the emulsion, the former addenda failing to exhibit antifoggant properties and the latter addenda severely desensitizing the emulsion after the one week incubation period at F. and 50% relative humidity.

Compounds A to E described above can be prepared by the methods described in Examples 2 to fi-below.

Example 2 2 Z-TETRAHYDROPYRANYL) BENZIMIDAZOLE To a mixture of 0.18 mole of o-phenylenediamine, 500 ml. of methanol and 0.40 mole of cupric acetate in one liter of water was added 0.23 mole of 2-forn1yltetrahydropyran. The mixture was stirred and heated at reflux on a steam bath of 2 hours, then allowed to stand at room temperature for about 16 hours. The copper salt was collected by filtration, washed with water, and suspended in one liter of 50% ethanol. The suspension was stirred and a slow stream of hydrogen sulfide gas was passed through over a 2.5 hour period. The resulting suspension Was then filtered through a steam heated Biichner funnel and the product crystallized yielding small colorless crystals, M.P. 236.0265.5 C., uncorr. A yield of 18% resulted.

Example 3 2- (2-PYRROLYL) BENZIMIDAZOLE The method described in Example 2 was repeated except that 2-pyrrolecarboxaldehyde was used in lieu of 2-formyltetrahydropyran. The product sublimed at 250 C./ 2 mm. and melted 278.0-2805 C., uncorr. A 50% yield was obtained.

Example 4 2- (2-THIENYL) BENZIMIDAZO'LE A mixture of 12.8 g. (0.1 mole) of 2-thiophenecarboxylic acid, 10.8 g. (0.1 mole) of o-phenylenediamine, and 100 ml. of 4 N hydrochloric acid was heated in an autoclave at 180-190 C. for one hour. Needles crystallized from the cooled mixture and were collected to yield 2.0 g. percent of theoretical). Recrystallization from acetic acid using Norit and sublimation in vacuum yielded colorless needles, M.P. 290 C., d. uncorr. (in a sealed tube).

Example 5 2- 2-TETRAHYDROFURYL) BENZIMIDAZOLE This was prepared in the same manner as the compound in Example 2 except that 2-formyltetrahydrofuran was utilized in lieu of 2-formyltetrahydropyran. yield was 66 percent of crude product, M.P. -2l0 C. Recrystallization from dilute ethanol yielded small colorless needles, M.P. 212.5-214.5 C., corr.

Example 6 2- (2-FURYL) BENZIMIDAZOLE A mixture of 3.60 g. (0.03 mole) of o-phenylenediamine and 5.85 g. (0.03 mole) of ethyl 2-furimidate hydrochloride in 25 ml. of ethanol was stirred for one hour, by the end of which time much presumed ammonium chloride had precipitated. While stirring, 50 m1. of water was added. The mixture was stirred for a few minutes more and filtered to obtain 4.40 g. (80 percent yield) of colorless microneedles, M.P. 292-293 C., uncorr.

The invention thus provides a new and useful class of photographic silver halide emulsion antifoggant addenda.

The invention has been described in considerable detail with particular reference to preferred embodiments thereof, but it will be understood that variations and modifications can be etfected within the spirit and scope of the invention as described hereinabove and as defined in the appended claims.

I claim:

1. A photographic silver halide emulsion containing a substituted benzimidazole antifoggant, said benzimida- The zole having substituted in the 2-position a heterocyclic radical having the formula wherein:

(a) X is selected from the group consisting of an oxygen atom, a sulfur atom and a nitrogen atom; and (b) Y is a hydrocarbon radical having 3 to 4 carbon atoms. 2. A photographic gelatino-silver halide emulsion containing about .001 to 10 grams per mole of silver halide in said emulsion of an antifoggant having the formula wherein:

(a) X is selected from the group consisting of an oxygen atom, a sulfur atom and a nitrogen atom; and

(b) Y is a hydrocarbon radical having 3 to 4 carbon atoms necessary to complete a heterocyclic ring.

3. A photographic gelatino-silver halide emulsion containing about .001 to 10 grams per mole of silver halide in said emulsion of the antifoggant, Z-(Z-tetrahydropyranyl)benzimidazole.

4. A photographic gelatino-silver halide emulsion containing about .001 to 10 grams per mole of silver halide in said emulsion of the antifoggant, 2-(2-pyrro1yl)benzirnidazole.

5. A photographic gelatino-silver halide emulsion containing about .001 to 10 grams per mole of silver halide in said emulsion of the antifoggant, 2-(2-thienyl)benzimidazole.

6. A photographic gelatino-silver halide emulsion containing about .001 to 10 grams per mole of silver halide in said emulsion of the antifoggant, 2-(2-tetrahydrofuryl)benzimidazole.

7. A photographic gelatino-silver halide emulsion containing about .001 to 10 grams per mole of silver halide in said emulsion of the antifoggant, 2-(2-fury1)benzimidazole.

8. A photographic emulsion support having coated thereon an emulsion as described in claim 1.

References Cited in the file of this patent UNITED STATES PATENTS 2,713,056 Sartori July 12, 1955 2,808,407 Ackermann et a1. Oct. 1, 1957 2,948,612 De Angelus et a1. Aug. 9, 1960 2,980,671 Nys et al. Apr. 18, 1961 

1. A PHOTOGRAPHIC SILVER HALIDE EMULSION CONTAINING A SUBSTITUTED BENZIMIDAZOLE ANTIFOGGANT, SAID BENZIMIDAZOLE HAVING SUBSTITUTED IN THE 2-POSITION A HETEROCYCLIC RADICAL HAVING THE FORMULA 